One of the things that I've never heard anyone talk about here, or in any other forum or rocketry group is why there isn't a "coasting smoke" delay grain in HPR motors? The coasting smoke grain should be part of the delay charge itself, much like BP motors use, so a person couldn't buy lower power motors, remove the smoke grain, and end up with a higher power motor, or combine them accidentally and end up with an under-powered motor.

Often I see videos of rockets that leap off the pad with clouds of smoke, but once the thrust is done, the rocket disappears (or nearly disappears) until the ejection charge blows. It seems to me that a grain of a material that doesn't add thrust, or only adds a little, but does add a visible smoke trail would be very useful for keeping HPR powered rockets in sight until the ejection charge blows. I'd also think it'd add a couple of safety factors for those who are unlucky enough to have a failure in the ejection charge of a motor-only deployment.

If the smoke isn't there, they have a visual clue that a failure is likely imminent.

They would know that at the site where the rocket impacted, there is still a live charge in and amongst the wreckage.

They could keep a better eye on where the rocket is at the moment of apogee, and perhaps allow them to better guesstimate where the rocket is going to impact the ground.

While I was typing this up, I suddenly realized that, to my knowledge, there is nothing stopping (outside of club regs) someone from assembling a higher power motor than they are supposed to be cleared for by combining multiple lower power motors. Not only would that be insanely stupid for the person who is doing it, it'd be dangerous for the people at the launch site, but could also result in severe problems for the hobby. I am now suddenly concerned for the S*****rm I might have just opened.

Well, in reverse, It's not hard to get high power motors without a cert....but it is hard to fly them without one....in theory you could order up a bunch of G79's, put them in a longer case with a longer liner.... but I don't think there's a bunch of people out there trying all that.

Erm..... HPR motors, DO have a delay grain...and even the Loki 54's I fly that don't have a delay.... have a smoke grain...

this is an HPR rocket much past burn out. If you don't see smoke, it's usually do to lighting issues....but it's there.

Well, in reverse, It's not hard to get high power motors without a cert....but it is hard to fly them without one....in theory you could order up a bunch of G79's, put them in a longer case with a longer liner.... but I don't think there's a bunch of people out there trying all that.

I'm presuming that the fool who is going to do something like that isn't going to stick around for a club launch. They're already rogue, and would likely do it at an unsanctioned event/site. It's not impossible for a person to buy or create their own HPR launch system.

Originally Posted by DavidMcCann

Erm..... HPR motors, DO have a delay grain...and even the Loki 54's I fly that don't have a delay.... have a smoke grain...

Then why do so many rockets seem to disappear once they reach the coast phase?

Another idea occurred to me... a "smoke only" motor. These would be designed for primarily for launches of scale rockets that have multiple motors (e.g. the Saturn V). The "core" motor would provide the go up power, whereas the others are purely for a more scale-like effect (and could be much smaller than the "core" motor).

kinda hard to see in the light, but this is that motor flying to 9,000' in a 2.6" screech-

But why isn't there a really clear smoke trail that extends all the way from the bottom of that picture to where it ends? I'm talking about a thick, very easy to see, full length smoke trail. I could imagine that the smoke's color could be matched to the color of the motor (Blue Thunder, White Lightning, etc.).

I'm presuming that the fool who is going to do something like that isn't going to stick around for a club launch. They're already rogue, and would likely do it at an unsanctioned event/site. It's not impossible for a person to buy or create their own HPR launch system.

Then why do so many rockets seem to disappear once they reach the coast phase?

Can't worry about everyone. they make their own choices.

They disappear mostly due to lighting. It's a thin smoke... not always as visible as other times...and typically better in person that on film.

There is smoke from the delay grain through out the coast. It cannot be seen because it is spread thin due to velocity.
Some research motors are made with full diameter delays (the delay is same diameter as motor grains), and the tracking smoke can be seen from burnout even at very high velocities. The down side is the heat from the delay grain usually ruins the temper in the case making it unusable a second time.

There is smoke from the delay grain through out the coast. It cannot be seen because it is spread thin due to velocity.
Some research motors are made with full diameter delays (the delay is same diameter as motor grains), and the tracking smoke can be seen from burnout even at very high velocities. The down side is the heat from the delay grain usually ruins the temper in the case making it unusable a second time.

M

Ok, now I'm getting an idea of why not...

I'm wondering how complicated it would be for a coasting smoke delay grain to be made that is larger than the typical delay grain, smaller than the full diameter grain, and not damage the case... Or how a disposable motor could be made for the desired effect (without all the added bonuses of knowing that failure is imminent).

I'm wondering how complicated it would be for a coasting smoke delay grain to be made that is larger than the typical delay grain, smaller than the full diameter grain, and not damage the case... Or how a disposable motor could be made for the desired effect (without all the added bonuses of knowing that failure is imminent).

The latest issue of the Tripoli Report tells how to make precisely that type of tracking grain. (Not used for ejection so it's not a delay grain.)

Best -- Terry

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It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so.
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----R. Heinlein

trying to control others actions and thinking they will affect us is a train of logic that leads to nothing but frustration and insanity. You simply can not prevent people from being stupid. It should not be assumed some idiot would close the hobby.

If the smoke was thick enough for that, it'd be something that generated thrust.

Another idea occurred to me... a "smoke only" motor. These would be designed for primarily for launches of scale rockets that have multiple motors (e.g. the Saturn V). The "core" motor would provide the go up power, whereas the others are purely for a more scale-like effect (and could be much smaller than the "core" motor).

Aerotech delay grains are exactly the same dimensions as 18,24,29mm propellant. It's all just blackjack.

Another idea occurred to me... a "smoke only" motor. These would be designed for primarily for launches of scale rockets that have multiple motors (e.g. the Saturn V). The "core" motor would provide the go up power, whereas the others are purely for a more scale-like effect (and could be much smaller than the "core" motor).

It's pretty routine for research motors. One just has to have a good enough liner. We generally aim for about 30 seconds of smoke trail, to cover the coast phase. That would be your typical big dumb rocket M through O east coast flight. It isn't a delay grain as generally electronics are used for larger rockets to control all the events.

Kosdon and I did a project and we were using 100 seconds of full diameter tracking smoke. 80 seconds to apogee plus 20 more to track on the way down and tell if the chute deployed. Yes single deploy. The paint was burned of the motor casing and top foot the aluminum soft.
All the research motors I have made had no tracking smoke. If it doesn't make it go higher I don't do it.

But why isn't there a really clear smoke trail that extends all the way from the bottom of that picture to where it ends? I'm talking about a thick, very easy to see, full length smoke trail. I could imagine that the smoke's color could be matched to the color of the motor (Blue Thunder, White Lightning, etc.).

The biggest reason there isn't a big clear smoke trail is because it's a large HPR. The very nature of larger motors makes it difficult to see the smoke because they are going faster and much higher then Estes and MPR sized motors. If you are flying Estes BP, you are probably limited to 1200 ft or so. It's easy to see the smoke trail at that distance. Most MPR motors stay below 3000 ft., many below 1500. Again it's relatively easy to see the smoke trail. When you have larger HPR motors at altitudes over a mile, it's not possible to put out enough smoke to make it "easily" visible that far away.

It isn't that HPR motors don't have smoke grains, it's that the nature and altitude of the HPR flights just makes the smoke much harder to see.

Another idea occurred to me... a "smoke only" motor. These would be designed for primarily for launches of scale rockets that have multiple motors (e.g. the Saturn V). The "core" motor would provide the go up power, whereas the others are purely for a more scale-like effect (and could be much smaller than the "core" motor).

MRC used to have the Smoke-FX motors that produced no thrust, only smoke. But not many rocket kit were made to utilize them. Anyway, the smoke produced thinned out significantly after the rocket started moving.

Best tracking smoke motors ever IMO were the longer AMW motors with full diameter grains. If you couldn't see that smoke, you couldn't see a rocket 10' in front of you.

But then you have the next guy saying that's a waste of propellant space. As an apples-to-apples comparison, the Loki 54-2800 motor uses the same dimension case as AMW 54-2550. Loki uses a forward bulkhead that takes the smoke grain out in front of the forward snap ring whereas AMW had the smoke within the length of the snap rings and full diameter at that. The difference is an extra ~2" of propellant in the Loki configuration.

So it's a tradeoff. For a given set of hardware, do you want more Newton-seconds of propellant or more tracking smoke? I'd venture that most would eye up the increased N-s and be satisfied with "just enough" tracking smoke.

Regarding "coasting smoke", for all practical purposes, the smoke grain is lit at the same time as the rest of the motor (endburners excluded). So that smoke is "on" the whole time. There may be a lull in density at burnout due to the drop in chamber pressure, plus that rocket is moving fast and thus the smoke is more thinly dispersed. Once the rocket slows, the smoke becomes denser. Don't know how else to explain it....

Generally with EX smoke grains, it is often a full diameter tablet grain with a layer of propellant of the appropriate web on top of a layer of smoke of the appropriate web for the desired smoke duration. The smoke is not burning while the motor is pressurized.

Generally with EX smoke grains, it is often a full diameter tablet grain with a layer of propellant of the appropriate web on top of a layer of smoke of the appropriate web for the desired smoke duration. The smoke is not burning while the motor is pressurized.

Gerald

Not to start an argument, but I don't believe K'tesh is speaking "EX" here. Alas, I wouldn't personally state that "generally EX smoke grains are full diameter with a layer of propellant....". I'm well versed in the arena and disagree with that generalization....maybe with your region/who you mix with, but not in general.

Regardless, your full diameter grain is burning while the motor is pressurized, whether you put a web thickness layer of propellant on the nozzle end of the grain or not.

The comment on a previous post was the smoke was burning. Hence, my clarification that it is not necessary that this be the case. Smoke is only "on" the whole time if it is designed to be. BTW, that quote isn't quite a quote of what I said. No matter though.

The comment on a previous post was the smoke was burning. Hence, my clarification that it is not necessary that this be the case. Smoke is only "on" the whole time if it is designed to be. BTW, that quote isn't quite a quote of what I said. No matter though.

Best tracking smoke motors ever IMO were the longer AMW motors with full diameter grains. If you couldn't see that smoke, you couldn't see a rocket 10' in front of you.

But then you have the next guy saying that's a waste of propellant space. As an apples-to-apples comparison, the Loki 54-2800 motor uses the same dimension case as AMW 54-2550. Loki uses a forward bulkhead that takes the smoke grain out in front of the forward snap ring whereas AMW had the smoke within the length of the snap rings and full diameter at that. The difference is an extra ~2" of propellant in the Loki configuration.

So it's a tradeoff. For a given set of hardware, do you want more Newton-seconds of propellant or more tracking smoke? I'd venture that most would eye up the increased N-s and be satisfied with "just enough" tracking smoke.

Regarding "coasting smoke", for all practical purposes, the smoke grain is lit at the same time as the rest of the motor (endburners excluded). So that smoke is "on" the whole time. There may be a lull in density at burnout due to the drop in chamber pressure, plus that rocket is moving fast and thus the smoke is more thinly dispersed. Once the rocket slows, the smoke becomes denser. Don't know how else to explain it....

You are correct sir.

I burned an old 54mm AMW K-1000 Skid at URRF at couple weeks ago, smoke all the way to 4,000+and a quarter of the way back down

I think one thing that also affects this is that for the most part, BP motors are end grain burning, and (again, for the most part) composite motors are not. End grain burning motors burn in sequence; thrust, smoke/delay, ejection. Composites burn all at the same time (in parallel).

I think one thing that also affects this is that for the most part, BP motors are end grain burning, and (again, for the most part) composite motors are not. End grain burning motors burn in sequence; thrust, smoke/delay, ejection. Composites burn all at the same time (in parallel).